乳脂酶解物对牛奶增香原理的探究

对添加稀奶油酶解物的90%脱脂乳感官明显提高的原理进行了探究。通过GC技术和固相微萃取(SPME)结合GC-MS的方法发现,作为乳类关键香成分的脂肪酸明显增加,其中,C8～C18的脂肪酸中偶数碳脂肪酸均有数倍增长;共检测到挥发性物质34种,其中特征性风味物质23种,对奶香贡献较大的脂肪酸类物质增长了83.9%,酮类增加了33%。因此,从机理上解释了增香90%脱脂乳风味提高的原因。     

乳酸菌发酵乳中挥发性风味物质的动力学分析

采用气相色谱技术对８个乳酸菌种（ＳＬ）发酵脱脂乳（１１％ＮＦＳ）后的６种风味物质进行了动力学分析。结果表明：嗜热乳杆菌发酵脱脂乳中各风味物质均高于乳球菌和干酪乳杆菌，在发酵２４ｈ时丁二酮的产量最高，以后较明显的下降，选出了ＳＴ－１与ＬＢ＿１为一对风味良好的酸奶菌株。此外，ＳＤ菌也是一种产香显著的嗜温菌，它与ＳＣ一样，在３０℃的产香力优于３７℃的产香力。     

不同干酪乳杆菌菌株对α-葡萄糖苷酶抑制作用的比较

从14株干酪乳杆菌中筛选出11株具有凝乳作用的菌株,采用以麦芽糖酶为靶向酶的α-葡萄糖苷酶抑制剂体外筛选模型,分析了不同干酪乳杆菌发酵脱脂乳上清对α-葡萄糖苷酶的抑制作用。结果表明,不同菌株发酵脱脂乳上清对麦芽糖酶的抑制活性具有明显的菌株特异性,且随着发酵时间延长,α-葡萄糖苷酶抑制活性呈现上升趋势。其中,干酪乳杆菌LC2W在37℃发酵10%(w/w)脱脂乳96 h后所得的上清液对麦芽糖酶抑制活性最高,达37.36%,明显高于其它被测试的干酪乳杆菌菌株,表明该菌株具有潜在的抗高血糖作用。     

蛋白酶和脂肪酶对稀奶油-乳清体系发酵特性及风味的影响

通过测定发酵过程中发酵动力学参数变化,利用顶空-固相微萃取和气相色谱-质谱法测定发酵60?h体系中挥发性风味物质,并进行主成分分析和感官评定,研究单独添加及复配添加蛋白酶和脂肪酶对稀奶油-乳清体系发酵特性及风味的影响。结果表明：风味物质以挥发性羧酸类、酮类和酯类为主。蛋白酶促进pH值下降、乳酸菌增殖和产酸,明显促进酮类生成,可增强体系的风味,提高风味品质;脂肪酶可引起滴定酸度大幅度上升,抑制乳酸菌增殖和产酸,但明显促进羧酸类生成,并产生酯类,可明显改变风味,赋予体系丰富的风味;复配添加后,结合2?种酶的特点,酯类产量上升,增香效果更明显,可显著改变风味,具有缓和大量挥发性羧酸带来的刺激性酸味作用。     

产脂肪酶菌株的筛选鉴定及产酶条件优化

以橄榄油为唯一碳源,采用油脂同化平板从食堂废弃物中筛选出一株产脂肪酶菌株HFE722。通过测定与分析该菌株16S rRNA基因序列,鉴定该菌株为芽孢杆菌（Bacillus sp.）。菌株HFE722在初始条件（发酵温度30 ℃,接种量为1%,自然pH,装液量为100 mL/250 mL,摇床转速为200 r/min）下培养36 h,测得发酵液上清液脂肪酶酶活为2.17 U/mL。优化后所得菌株HFE722产酶的最适发酵条件为：发酵温度30 ℃,发酵周期为36 h,接种量为1%（V/V）,初始pH 7.0,装液量为50 mL/250 mL,摇床转速为160 r/min。在最佳发酵条件下,发酵液上清液酶活可达到5.8 U/mL,酶活较优化前提高了167.28%。     

蓝莓采后病原菌胞外脂肪酶的提取及粗酶性质研究

以蓝莓采后主要病原菌灰霉为试验菌株，通过单因素试验对其培养基成分和发酵条件进行优化，并研究其酶学性质。结果表明，采用含橄榄油1%、蛋白胨1%，pH 7.0的PDA培养基，发酵温度25 ℃，发酵时间96 h时，灰霉菌具有最高的产胞外脂肪酶能力。酶学性质研究表明，该脂肪酶对pH和温度的适应范围较宽，在40 ℃、pH 9.0的反应条件下，粗酶的脂肪酶活性最高；Na+、Fe3+能促进粗酶的活性，K+、Ca2+、Mg2+、Cu2+则抑制粗酶的活力；该粗酶在一定体积分数的异丙醇、甲醇、丙酮中具有良好耐受性，而在乙酸乙酯和二甲苯中处于激活状态。优化使病菌灰霉菌脂肪酶的产率增加，为后续脂肪酶的分离纯化奠定基础。初步探讨胞外脂肪酶的粗酶性质，为蓝莓采前病害防治及采后品质保护提供科学依据。     

红曲霉固体发酵生产酿造增香发酵剂的研究与应用

该文阐述了有多酶系的红曲霉菌株ZH-4的筛选优化过程,研究了该菌株固体发酵生产酿造增香发酵剂的工艺条件,并对工艺参数进行了优化.同时,对酿造增香发酵剂在酿造产品生产中的应用做了研究,对酱油和醋等酿造产品的风味和感官有一定改善的同时还提高了生产原料中淀粉和蛋白质的利用率.     

气相—嗅闻法分析奶油酶解产物中的特征风味组分

奶油酶解增香研究主要是以奶油或无水奶油为原料,利用脂肪酶酶解乳脂肪,通过控制酶解条件,得到不同香气特征的酶解产物。采用顶空固相微萃取法(HS-SPME)提取酶解奶油产物的风味物质,通过气-质联用结合气相-嗅闻法(GC-O)分析酶解奶油样品的特征风味成分,确定其中的主要呈香物质以及各物质对风味的贡献度。通过嗅闻实验最终检测到17种与样品风味有对应关系的挥发性物质,其中丁酸、己酸、癸酸、辛醛、柠檬烯、辛酸、己酸乙酯、δ-己内酯、乙酸、己酸丁酯等组分的气味强度较高,是酶解奶油产物的主要呈香组分。     

酶解对霉菌发酵乳风味的影响

以霉菌发酵乳为原料,以游离脂肪酸含量和游离氨基酸含量为检测指标,研究脂肪酶和蛋白酶的酶添加量、酶解温度、酶解时间3个因素对发酵乳风味的影响。结果表明,最优酶解条件为脂肪酶添加量1.5%,酶解温度45 ℃,酶解时间5 h,在此条件下游离脂肪酸含量为8.17%;蛋白酶添加量0.15%,酶解温度55 ℃,酶解时间5.5 h,在此条件下,游离氨基酸含量为0.41%。说明酶解可有效增加霉菌发酵乳风味物质,为进一步增强牛乳风味的研究与应用提供了基础。     

多轮增香发酵对传统榨菜风味成分影响研究

以四川传统特色发酵食品榨菜为研究对象,分析鉴定普通榨菜、多轮增香发酵榨菜发酵前后的物质成分变化。采用气相色谱-质谱连用技术对普通榨菜与多轮增香榨菜的风味成分进行鉴定和分析,探讨多轮增香发酵工艺对榨菜发酵风味物质的影响。结果表明,普通榨菜共识别出24种化合物,多轮增香发酵榨菜共识别出30种化合物,主要是醇类、醛类、酮类和酸类等,它们的协同作用构成了榨菜特有的香味成分,而且多轮增香发酵榨菜的风味更好。     

不同脂肪酶酶解奶油制备奶味香基的研究

选用Hansen calf lipase、Amano lipase A6、Lipozyme RM IM 3种脂肪酶对无水奶油进行适度酶解制备奶味香基。采用气相色谱分析了酶解奶油中游离脂肪酸组成,结合顶空固相微萃取-气相色谱质谱联用技术对酶解奶油中的挥发性风味成分进行研究,并通过感官评价对酶解奶油进行风味剖面分析并对烘焙产品偏好性评定。结果表明:3种脂肪酶选择性酶解产生中短链脂肪酸的能力均较强,其中动物来源的Hansen calf lipase对中短链脂肪酸的选择性酶解能力最高,酶解奶油中短链脂肪酸相对含量为42.9%,且该酶解奶油和烘焙产品具有令人愉悦的奶味和干酪味;3种酶解奶油中的挥发性风味成分主要为脂肪酸、醛类、酮类、内酯类物质。     

UHT乳贮存期间脂肪变化的研究

在UHT乳贮存期间,对其脂肪酶活力、上层脂肪含量、上层脂肪粒径、游离脂肪酸含量进行测定。结果表明,随着贮存时间的延长,脂肪酶活力、上层脂肪含量、上层脂肪粒径、游离脂肪酸含量变化极显著(P<0.01);贮存时间与脂肪酶活力、上层脂肪含量、上层脂肪粒径、游离脂肪酸含量间均呈极显著正相关(P<0.01)。     

Acceleration of Cheddar Cheese Lipolysis by Using Liposome-entrapped Lipases

ABSTRACT: Two types of lipase (Palatase M and Lipase 50) were encapsulated in liposomes with trapping efficiencies of 35.9 and 40.3%, respectively. The lipases were incorporated into cheese milk at levels of 0.2, 0.5, and 1.0 lipase units/g fat. Treated cheeses had higher moisture and lower protein, fat, and ash contents than the control cheese and they were less firm, but more elastic and cohesive, than the control cheese. Production of free fatty acids was accelerated by the addition of encapsulated enzymes. Cheeses with up to 0.5 lipase unit/g milk fat had slightly better flavor intensities than control cheese. Cheeses with the highest level of Palatase M and Lipase 50 developed a pronounced soapy off-flavor after 2 and 3 mo of ripening, respectively.     

脂肪酶水解乳脂制备天然奶味香基的研究

选取了5种微生物来源的脂肪酶对乳脂进行酶解。结合香气评定,筛选出了对乳脂中短链脂肪酸特异性最强、水解物香气评分最高的lipase MER为实验用酶。研究了lipase MER水解乳脂的工艺条件,得出其水解乳脂适宜温度为40℃、pH值为6.5,底物浓度为50%。经焙烤评定lipase MER水解乳脂制得的水解物奶香柔和、自然。可作为调配天然奶味香精的香基。     

Effects of cyclodextrins on the flavor of goat milk and its yogurt

Goat milk fat includes several branched chain fatty acids (BCFAs), like 4-methyloctanoic acid, which when free, are responsible for goaty flavor. This flavor limits the market opportunities for goat milk. Prior research showed that cyclodextrins (CDs) can reduce goaty flavor, presumably by binding free fatty acids. This research extends that observation. In odor ranking trials in citrate buffer at pH 4.8, β-CD concentrations between 0% and 0.35% were increasingly effective in reducing odor intensity due to 4-methyloctanoic acid, but only when present in high molar excess. α-CD was also effective, but γ-CD was not. In lipase-treated goat milk only β-CD was effective but at much lower molar excess, a difference potentially explained by several factors. One was that BCFAs bind to CDs in marked preference to their straight chain isomers. Displacement experiments with phenolphthalein disproved that hypothesis. The ability of β-CD to reduce goaty flavor intensity extended to yogurt. An analytical panel showed that flavor of goat yogurt was reduced by addition of β-CD, but only if added before heating and fermentation. A hedonic trial showed that consumers preferred unsweetened and sweet/vanilla-flavored goat yogurt more when β-CD was included, P = 0.004 and 0.016, respectively. Males liked all yogurts more than females (P < 0.01), but there was a treatment × gender interaction (P = 0.016) for sweet/vanilla yogurt: sweet/vanilla masked the goaty flavor for males but not females. This results parallels previously demonstrated gender effects for sheepmeat flavor caused by BCFAs. PRACTICAL APPLICATION: β-Cyclodextrin masks goaty flavor in yogurt, and with its GRAS status means it could be used in commercial goat yogurts and similar products so the real or perceived nutritional advantages of goat milk are not lost to goaty flavor.     

EFFECT OF LIPASE ENZYME ON THE RIPENING OF WHITE PICKLED CHEESE

The effect of addition of pregastric lipase enzyme on the accelerated ripening of white pickled cheese was investigated. Commercial pregastric lipase was added to milk before rennet addition at a level of 0,5, 8, 11 g per 100 L of milk and cheeses were made from this milk. Total solids, fat, total nitrogen, salt, titratable acidity, pH and free fatty acids (C₂-C_18:1) were analysed in the samples during 1–90 days of ripening period at 15 days intervals. Total solids, fat, total nitrogen, salt, titratable acidity, and pH of cheeses slightly increased during the ripening period. Free fatty acids and volatile free fatty acid contents in cheeses made from pregastric lipase added milk were affected by pregastric lipase and their contents were increased significantly (P<0.01) during the ripening period. Particularly, when cheese had a high level (11 g per 100 L milk) pregastric lipase, the amounts of butyric, caproic and caprylic acids in white pickled cheese were quite high. The relative amounts of volatile free fatty acids varied with storage time and pregastric lipase levels.     

Feeding a concentrate rich in rapeseed oil improves fatty acid composition and flavor in Norwegian goat milk

Impaired quality due to a high content of free fatty acids (FFA) and off-flavors has caused challenges in the development of Norwegian goat milk products. The present study aimed to examine the effect of lipid-supplemented concentrates on milk fat content, fatty acid composition, FFA, lipoprotein lipase activity, sensory properties, and size of milk fat globules of goat milk. Thirty goats assigned to 3 experimental groups were fed different concentrates from 60 d in milk (DIM) until late lactation (230 DIM). The diets were (1) control concentrate (no added fat); (2) control concentrate with 8% (added on air-dry basis) hydrogenated palm oil enriched with palmitic acid (POFA); and (3) control concentrate with 8% (added on air-dry basis) rapeseed oil (RSO). The POFA group produced milk with the highest fat content, and fat content was positively correlated with the mean size of milk fat globules. Goats in the RSO group had a higher content of long-chain and unsaturated fatty acids, whereas milk from goats in the POFA group had a higher content of palmitic and palmitoleic acids (C16:0 and C16:1 cis). The control group produced milk with a higher content of short-, medium-, odd-, and branched-chain fatty acids compared with the 2 other groups. The content of FFA in milk was low in early and late lactation and peaked in mid lactation (90 DIM). A high content of FFA was correlated with poor sensory properties (tart/rancid flavor). The RSO group produced milk with lower content of FFA and off-flavors in mid lactation and a higher proportion of unsaturated fatty acids. Therefore, replacement of palm oil with rapeseed oil as a lipid source in dairy goat feed would be favorable.     

酶促奶油水解制备天然奶味香精

选用脂肪酶lipaseAY水解奶油制备天然奶味香精。在奶油与乳清粉的质量比为14:1,脂肪酶量为奶油质量的0.2%,反应温度为45℃时,其香气评分最佳。GC-MS分析结果显示:产物中脂肪酸约占80%,内酯和酯类约为20%。所制备的天然奶味香精具有浓郁的干酪风味,带有淡淡的甜奶香味,香气醇厚,口感细腻。另外,适量添加乳清粉有利于改善产物口感。     

微生物发酵与酶法结合制备天然奶味香基的研究

选用具有丁二酮合成能力的乳酸乳球菌NRRL B-2356发酵全脂乳与脂肪酶结合制备天然奶味香基。乳酸乳球菌NRRL B-2356发酵全脂乳丁二酮、3-羟基丁酮产量在27h时达最大(52.95μg/mL),与德氏乳杆菌混合发酵,两者接种量比值为5:1时,丁二酮、3-羟基丁酮含量达60.1μg/mL,香气评分最高。利用脂肪酶palatase2000L对发酵液进行酶解修饰以提高香气强度,酸值为6.73mgKOH/g时香气评分最高。同时蒸馏萃取装置与GC-MS结合对奶味香基中挥发性成分进行了分析,结果表明,游离脂肪酸为98.586%,酮类1.219%,内酯类0.142%。研究制备的奶味香基香气纯正浓郁,可用于调配高档奶味香精。